Glass substrates such as those utilized in flat panel displays and other electronic devices are generally formed from a large glass substrate which is segmented into a plurality of smaller glass substrates that are incorporated into individual devices. A variety of separation techniques may be used to separate the large glass substrate into a plurality of smaller glass substrates including laser cutting techniques. In order to separate a glass substrate by laser cutting, an initiation defect or vent crack may first be formed in the glass substrate using a single point scribe. To form the initiation defect the scribe is brought into contact with the glass substrate and a force which is normal to the surface of the glass substrate is then applied to the scribe, pressing the scribe into the surface of the glass substrate. The force exerted on the scoring wheel creates an initiation defect that extends partially through the thickness of the glass substrate. Thereafter, the initiation defect is heated and rapidly cooled to propagate a through vent from the initiation defect to separate the glass substrate.
While a scribe may be used to create an initiation defect, such single point initiation defects can require careful alignment between the initiation defect and the laser in order to heat locally at the initiation defect. This can require precise control of the glass substrate in the machine cross or lateral direction to avoid initiation defect misalignment. Use of various conveyance systems, such as air bearings can further complicate lateral movement control of the glass substrate between the initiation defect forming location and the laser source.
Accordingly, a need exists for alternative methods and apparatuses for creating crack initiation defects in thin glass substrates to facilitate separating the thin glass substrates into a plurality of individual glass substrates by laser separation.